Fluid flow sensor having light reflective slider

ABSTRACT

A flow sensor for detecting the absence of a minimum fluid flow in a sprinkler system. The fluid acts upon a vane positioned in the fluid path. Movement of the vane controls the position of a slider. The slider&#39;s surface has reflective and nonreflective ends which, in response to the vane&#39;s movement reflect or absorb light from a light emission and detection means. The voltages from the light emission and detection means are monitored for indications of the fluid flow. The sensor uses a two wire signal transmitting system.

In a particular aspect this invention relates to sensing water flow inpipes associated with a building fire sprinkler system. However, theflow sensor of the present invention has other applications such as inrespect of oil refineries, gas plants and pumping systems.

Building fire sprinkler systems usually comprise a main pipe which feedsto sub-main pipes which in turn feed to individual sprinkler pipes. Itis known to place flow sensor devices at least in each sub-main pipe andalso in each individual sprinkler pipe.

A known flow sensor includes a paddle which, when moved by water flowingin an associated sprinkler pipe, will move a mechanical switch tocomplete an electrical circuit.

For reasons of safety, it is not considered satisfactory that a knownsensor should close a switch in a two wire system consisting of a powersupply wire and a return wire as any break in either of the wires or inan associated connection would render the closing of the switchineffective.

Instead, a three wire system is used in which two wires are respectivelya power supply and return wires and the third wire is a signal carrywire through which current passes when the switch is closed. A loadresistor is located adjacent the sensor and a small current iscontinually passed through the supply and return wires. The three wiresrun to a remote monitor panel where current sensor means is located andadapted to give an alarm in the event that current flow in the supplyand return wires exceeds a first value (as may occur in a short circuit)or falls below a second value (as may occur in an open circuit). Othercurrent sensor means is adapted to give a signal if current flows in thesignal carry wire.

It is particularly to be noted that whilst the integrity of the supplyand return wires is continually monitored, the integrity of the signalcarry wire is not continually monitored. This last is considered by thepresent inventors to be an unsafe practice.

Further, since three wires must be run from each sensor to the controlpanel there is substantial cabling expense.

Further, the known sensor utilizing a mechanical switch is considered bythe present inventors to be unsatisfactory.

It is one object of the present invention to produce a flow sensor foruse in a two wire system. However, it is also another object of thisinvention to produce a flow sensor having other features and which couldbe used in a conventional three wire system.

The present invention provides:

a flow sensor comprising a body,

a partition dividing the body into first and second ends, the partitionbeing fluid tight and being or comprising a window, light emission meanslocated in the first end and adapted to transmit light through thewindow towards the second end, a surface having a substantially lightreflective portion and a substantially light unreflective portionlocated in the second and adapted to be moved between first and secondpositions with respect to the window in which it will, respectively,substantially reflect light from the light emission means back throughthe window towards the first and substantially not reflect light backthrough said window towards the first and,

a light detector means located in the first end and adapted to producean output signal when receiving light reflected through said windowtowards the first end by said surface when in the first position,wherein the second end is adapted to be connected to a pipe or otherstructure within which fluid may flow and mechanical means movable inuse by fluid flowing in said pipe or other structure and operative whenso moved to move said surface from said second position to said firstposition.

Preferably said surface and said window are so closely spaced or saidsurface carries wiping means adapted to contact the window such thatsaid surface or said wiping means will produce a cleaning wiping effecton said window in being moved from the second position to the firstposition.

The mechanical means is preferably a vane mounted to pivot about anaxis.

The mechanical means is preferably enclosed by a sealing member such asa flexible boot such as of rubber.

Said surface is preferably silvered in one region to be reflective inthat region and black in another region so as not to be reflective inthat region.

The sensor of the present invention may be used in a flow sensor systemsuch as a three wire building fire sprinkler alarm system and in thisrespect the light emission means may be connected to current supply andreturn wires and the light detector means may be connected to a third,signal carry wire.

However, as is preferred, the sensor of the present invention may beused in a two wire flow sensor system such as a building fire sprinkleralarm system in which the two wires are used as current supply andreturn wires and as a signal carrier.

In this respect, if the sensor of the present invention is tocontinuously monitor, as is usual although intermittent monitoring ispossible, the light emission means may be connected across currentsupply and return wires. In this condition, a cable monitoring end ofline resistor may be omitted if desired as the light emission means willinter alia act as that resistor. However, the end of line resistor maybe maintained if desired. In this condition if the light emission meansshould fail and go open circuit, the resistance in the system willchange and this can be detected at a remote monitor means; if the lightemission means should fail and go to short circuit, the resistance inthe system will also change and this too can be detected.

The output from the light detector means can be connected to either ofthe current supply and return wires and when outputting will alter theresistance of the system which again can be remotely detected.

Such changes in resistance may be detected by voltage or current monitormeans.

Accordingly, the present invention also provides a two wire buildingfire sprinkler alarm system incorporating a sensor in accordance withthis invention.

The present invention also provides a flow sensor having a lightemission means and a light detector means and constructed and arrangedsuch that on a predetermined flow condition occurring light from thelight emission means will be detected by the light detector means, andincluding first and second circuit elements effective in use as currentsupply and return means and as a signal carrier and wherein the lightemission means is connected across the current supply and return meansand constructed and arranged such that if the light emission meansshould fail and go open circuit, the resistance of the sensor willchange; if the light emission means should fail and go to short circuit,the resistance of the sensor will change and such that the output fromthe light detector means can be applied to either of the current supplyand return means and when outputting the resistance of the sensor willchange.

The present invention also provides a flow sheet sensor systemincorporating a flow sensor having a light emission means and a lightdetector means and constructed and arranged such that on a predeterminedflow condition occurring light from the light emission means will bedetected by the light detector means, the system including first andsecond circuit elements to be used as current supply and return meansand as a signal carrier and wherein the light emission means isconnected across the current supply and return means and constructed andarranged such that if the light emission means should fail and go opencircuit, the resistance in the system will change such as to bedetectable at a remote monitor means; if the light emission means shouldfail and go to short circuit, the resistance in the system will changesuch as to be detectable at said monitor means and such that the outputfrom the light detector means can be connected to either of the currentsupply and return means and when outputting will alter the resistance ofthe system such as to be remotely detectable at said monitor means.

Another problem of the known sensor discussed above is a tendency togive false alarm signal due to fluctuations in mains pressure, waterhammer or during testing.

Accordingly, it is preferred that circuit means be associated with thesensor which is adapted to delay outputting of an output signal unless acondition initiating an output signal is maintained for not less than apredetermined period of time.

In this last instance it is preferred that output from the lightdetector means be directed to a timing circuit which will only producean output for signaling purposes if the output from the light detectormeans is maintained for more than said period of time.

As well as an ability to give a signal to a remote control panel it isalso desirable that the sensor of this invention be adapted to give, ator adjacent the sensor, a visually or audibly perceivable signal of thefact that it is giving such a signal to the panel.

This last will be found to be useful when a serviceman or like isadjacent the sensors and remote from the panel in quickly detectingwhich one of many sensors is outputting.

A specific construction of a fluid flow sensor in accordance with thisinvention will now be described with the aid of the accompanyingdrawings in which:

FIG. 1 is a cross-sectional view of the sensor, and

FIG. 2 is a circuit diagram of circuitry of the sensor.

The sensor shown in FIG. 1 comprises a metal body 1 having a screwthreaded end 2 whereby it may be connected to a pipe through which fluidmay be expected to flow.

Within the body 1 is a shoulder 4 carrying an O-ring seal 6 andsupporting a transparent sheet 7 of plastics material. A screw threadedmember 8 having an aperture 9 is screwed into the body 1 and partitionsthe body into a first end 22 and a second end 23.

Various electronics are located in the first end 22 and inter aliacomprise a light emitter 25 and a light detector 26. The first end isclosed by a screw threaded cap 27 which bears on a body 5 having asealable hole 28 through which a twin cable may pass. An O-ring seal 21is provided.

The second end (23) includes a flow detector mechanism comprising apivot axis 31, an arm 32 mounted to pivot on the pivot axis 31, a vane33 at one end of the arm 32 and a slider 34 adapted to be moved by thearm 32.

A rubber boot 37 held by split circular clip 38 will help to keep dirtout. Alternative seals to the boot 37 may be provided.

The slider 34 is black at its end 41 to be non-reflective and silveredat its end 42 to be reflective.

The slider 34 and arm 32 are biased to the positions shown in FIG. 1 bya spring 36. Further the slider is biased towards contact with the sheet7 by a spring 44 which acts on a ball carrier 43. Movement of the slider34 will tend to wipe clean the sheet 7.

In use, fluid in flowing will act on the vane 33 to move the arm 32 tomove the slider 34 such that instead of the black and 41 being in aposition adjacent the aperture 9 the silvered end 42 will be in aposition adjacent the aperture 9. In the latter position but not in theformer position light from the emitter 25 will be reflected by thesilvered end 42 to the detector 26.

Reference is now made to FIG. 2.

The circuit of FIG. 2 is a sensor circuit located within the sensor body1 and is to be connected to wires 61 and 62 of a two wire system in abuilding fire sprinkler alarm system. The wire 61 is a nominal positive,the wire 62 is a nominal negative, an end of line resistor (EDL) isprovided and terminals a,b and c are provided for connection toterminals A,B and C of the sensor circuit.

The sensor circuit comprises an LED1 an infrared light emitting diodewhich is the light emitter 25 and a protective diode D1 which willprotect against reverse polarity. Further, in the event of a reversepolarity connection, the diode D1 will short circuit and this will causea detectable current flow in the wires 61 and 62. In addition, a voltagelimiting Zener diode ZD1 and a voltage limiting resistor are provided tolimit current flow. A jumper J1 is normally positioned to connectterminals D and F.

Under normal conditions without flow of water in a pipe with which thesensor is associated only LED1 will be energised and thus current flowwill be small. It will thus be realized that current flow to check theintegrity of the wires 61 and 62 through the EDL resistor will alsodrive LED1 and, further, if LED1 should fail by going open circuit orshort circuit then current flow will change in a way which can bedetected.

Under normal conditions, light from LED1 will be incident on black end41 and not be reflected but if the slider 34 has been moved by the arm32 in consequence of water flow light will be reflected from silveredend 42 onto PT a phototransistor which is the light detector 26.

When light strikes PT it becomes conducting and via transistors T1 andT2 there is amplification of the current flow in PT. Resistor R1provides negative feedback to reduce gain.

The output of T2 is connected as an input signal to, and power sourcefor, IC1 which is a 3905 precision timer. Thus, prior to T2 output,which is dependant on PT conducting, the timer IC1 is not energised andis consuming no current.

R5 is a variable resistor and C1 is a capacitor which together form a RCtiming circuit. By adjustment of R5 the timing is varied.

Provided that output from PT and hence T2 is maintained for more thanthe time period set by R5 and C1, the IC1 will output at terminal 7 totransistor T3. If, however, PT should cease outputting before that timeperiod has elapsed, as might be the event in a potential false alarmcondition, no output to T3 will occur and thus false alarms areunlikely.

Output from T3 passes via a current limiting resistor R3 to LED2 whichis a light emitting diode. This may be omitted but is usefully mountedoutside or to be viewable from outside the sensor body 1 to give avisual indication that the particular sensor is outputting. This last isdesirable as in a large building with many such sensors the fact that aremote control panel is indicating that a particular sensor isoutputting is of little help to a serviceman who is not adjacent thatremote control panel but is adjacent to a number of sensors and isuncertain as to which of them is outputting.

Output from T3 also passes through current limiting resistor R4,terminals B and b and wire 62 to give a detectable current flow at theremote monitor panel.

Resistor R2 will allow the timer IC1 to reset after testing.

The above described flow sensor and its circuit will find goodapplication in building fire sprinkler alarm systems and also in otherapplications of fluid flow monitoring.

With jumper J1 connecting terminals D and F the flow sensor will be ableto act as a supervising monitor in which its own circuit is alsosupervised.

However, if jumper J1 is removed and in lieu a jumper J2 is used toconnect terminals D and E then the circuit is no longer monitored butthe sensor can be used to directly control a relay or other switchingdevice for giving a signal or operating means which as might be requiredin an airconditioning plant and in this instance resistor R7 serves as acurrent limiting resistor for LED1.

In a modification, a coil spring mounted on the axis 31 is used in lieuof the spring 36.

The claims form part of the disclosure of this specification.

Since modifications within the spirit and scope of the invention may bereadily effected by persons skilled in the art, it is to be understoodthat the invention is not limited to the particular embodimentdescribed, by way of example, hereinabove.

The claims defining the invention are as follows; we claim:
 1. A flowsensor comprising:a body, a partition dividing the body into first andsecond ends, the partition being fluid tight and capable of transmittinglight, light emission means located in the first end and adapted totransmit light through the partition toward the second end, slider meanslocated in said second end and adapted to be moved between first andsecond positions with respect to the partition, said slider means havinga surface substantially abutting said partition and having asubstantially light reflective portion and a substantially lightunreflective portion which will, respectively, substantially reflectlight from the light emission means back through the partition towardsthe first end when said slider means is in said first position andsubstantially not reflect light back through said partition towards thefirst end when said slider means is in said second position, a lightdetector means located in the first end and adapted to produce an outputsignal when receiving light reflected through said partition toward thefirst end by said surface when in the first position, wherein the secondend is adapted to be connected to a pipe or other structure within whichfluid may flow, and mechanical means incorporated in said second end andmovable, in use, by fluid flowing in said pipe or other structure andoperative when so moved to move said slider means from said secondposition to said first position.
 2. A flow sensor according to claim 1,wherein said surface is so formed as to contact the partition andproduce a cleaning wiping effect on said partition when being moved fromthe second position to the first position.
 3. A flow sensor according toclaim 1, wherein said surface is silvered in one portion to bereflective in that portion and black in another portion so as not to bereflective in that portion.
 4. A flow sensor comprising: a body,apartition dividing the body into first and second ends, the partitionbeing fluid tight and capable of transmitting light, light emissionmeans located in the first end and adapted to transmit light through thepartition toward the second end, a surface having a substantially lightreflective silvered portion and a substantially light unreflective blackportion, said surface being located in the second end and adapted to bemoved between first and second positions with respect to the partitionin which it will, respectively, substantially reflect light from thelight emission means back through the partition toward the first end andsubstantially not reflect light back through said partition toward thefirst end, a light detector means located in the first end and adaptedto produce an output signal when receiving light reflected through saidpartition toward the first end by said surface when in the firstposition, wherein the second end is adapted to be connected to a pipe orother structure within which fluid may flow, and mechanical meansincorporated in said second end and movable, in use, by fluid flowing insaid pipe or other structure and operative when so moved to move saidsurface from said second position to said first position.